1. Field of the Invention
The present invention is related to an overloading limitation of a switched-mode power supply (SMPS).
2. Description of the Prior Art
A power supply is a kind of power management device that transforms power from a power source to provide transformed power to an electronic device or component. FIG. 1 illustrates conventional power supply 60, which employs a flyback topology. In FIG. 1, bridge rectifier 62 is utilized for rectifying AC power VAC to provide input power VIN to transformer 64. When switch 72 is close-circuited, primary winding Lp of transformer 64 is charged. When switch 72 is open-circuited, secondary winding Ls of transformer 64 discharges to load capacitor 69 via rectifier 66 to generate output power VOUT. Error amplifier EA compares voltage levels of output power VOUT and target voltage VTARGET to generate a compensation signal Vcom. Controller 74 controls switch 72 with the aid of control signal VGATE according to both compensation signal Vcom and current detection signal Vcs, which correspond to inductive current flowing through primary winding Lp.
Many types of protection may be added to power supply 60, including over-voltage protection (OVP), over-temperature protection (OTP), and overload protection (OLP). Overload protection is used when output current loading of power supply 60 is too high, and when the power supply provides power exceeding a predetermined output power level.
Overload protection may be implemented by limiting output current, or by limiting the inductive current flowing through primary winding L. Both implementations are intended to prevent power outputted by the power supply from exceeding a certain level.